Abstract:

CuGaSe₂/CuInSe₂ tandem junction solar cell is currently being pursued to
be a low cost and high efficiency renewable energy source. A reported theoretical
efficiency of 33.9% solar cells has been the motivation to fabricate CuGaSe₂ films
in a simple and low cost method. Electrodeposition is a potentially suitable
method to obtain the CuGaSe₂ films. A better understanding of the
electrodeposition process is required to optimize the process.
Focusing on the manufacture of CuGaSe₂ film, the reaction accompanying
the electrodeposition of CuGaSe₂ using rotating disk electrode from cupric
sulfate, selenious acid and gallium chloride solution in sulphate medium were
studied by voltammetry. Cyclic and rotating disk voltammetry in pure and binary
systems were performed in order to understand the complexity of Cu + Ga + Se
systems. Diffusion coefficients of Cu(II) and Se(IV) were determined using
Levich equation to be 6.93x 10⁻⁶ cm²/s and 9.69x 10⁻⁶ cm²/s, respectively.
The correlations between supporting electrolytes, flux ratios, working
electrodes and films were investigated experimentally. The deposited films were
characterized by Induced Couple Plasma Spectrometry, X-Ray Diffraction,
Scanning Electron Microscopy and Energy Dispersive X-Ray. CuGaSe₂ is formed
via the reaction of CuSe compound reduction and Ga(III) and higher gallium
concentration will favor the formation of CGS film. The incorporation of gallium
is highly depending on the pH (higher is better).
An impinging flow electrochemical reactor was built as an alternative
approach for electrochemical deposition method. Preliminary experiments of
copper and copper selenide electrodeposition were conducted, and the results
were comparable to the rotated disk voltammetry.